Hello:
We are using a few VNAs with options 080 and 082 to make measurements of high power Block Upconverters (BUCs), and at the moment we are considering whether to update another analyzer for similar SMC type measurements.
A question came up whether option 084 would be more suitable. While the BUCs do have embedded LOs, the description of the option appears to just offer the capability of group delay measurement with a simplified setup. Our typical application is simply to measure frequency translated gain. Does option 084 offer any other functionality to assist that?
Another question regarding options 080 and 082. Many, many years ago, when these options were evaluated on N5230s, there appeared to be little support to calibrate out any adapters attached to the BUCs. For example, it is typical to use a coupler at the output of 40 dB or more to interface with the analyzer. Attempts to calibrate it out, or to de-embed the coupler typically resulted in a noisy measurement. We got around this by using adapters with very flat responses. Have we missed something here, or perhaps the modern versions of options 080 and 082 on more recent VNAs have better support for this kind of application?
The key capability in option 084, is the ability for the SMC channel to correct errors in the LO frequency (error = difference between the LO frequency value entered in the mixer setup and the actual LO frequency generated by the embedded LO) and realign the VNA internal LO frequency so that the VNA's output receivers is properly centered at the converter's output frequency. If the LO error is small (the error in Hz is a small fraction of the IFBW being used for the measurement) and the error is constant (the embedded LO drift rate is at least an order of magnitude greater than the measurement sweep time) then the effect on the converter gain measurement will be very small (basically the error in gain or output power measurement will be proportional to the insertion loss of the IFBW filter relative to the center of the filter at an offset equal to the LO error). In the PNA, you can actually measure the shape of our IFBW filters by using FOM ( I am not going to get into the details of how to make that measurement unless you are interested in doing it).
While without option 084 and a converter with an accurate and stable embedded LO circuit, you could easily make "good enough" gain measurements, even a small magnitude error would create significant phase and therefore group-delay error, which is why we recommend using option 084 if you are making group delay measurements. Hopefully this can help you decide if you do or do not need option 084. Also keep in mind that option 084 is software only and therefore can be added anytime after you purchase your new system if your measurement requirements change.
As to your other question about dealing with high loss external couplers for high power measurements, we have made significant improvement in the de-embedding process (i.e we have made it easier to manage the logistics of setting up de-embedding with the introduction of Cal Plane Manager feature), but the measurement fundamentals are still the same and de-embedding a 40 dB coupler from a full 2-port correction (in SMC or any other measurement that supports 2-port corrections) is still going to result in potentially noisy measurements. the best remedy for those scenarios is using what we call an Enhanced Response correction, whereby we correct for the input match of the DUT and the transmission response, but do not correct for the output match (should be very good with a 40 dB couple attached to the output). In SMC, you can access that correction type by going to the Correction Methods dialog and making the following selections:
In terms of performing the calibration, you can perform a normal full 2-port SMC calibration without the output coupler and add it back in, do the de-embedding and change the correction type as I showed above.